1. Field of the Invention
This invention relates to an improved pressure rebalance system for measuring fluid flow and more particularly to such a system which is sealed and thus will not become clogged by particulate matter in the fluid whose flow is being measured.
2. Description of the Prior Art
As it is well understood by those skilled in the art, fluid flow through an orifice, venturi, or other restriction produces a pressure drop which is proportional to the square of the volume rate of flow. Thus, the pressure drop created by the flow through the orifice or venturi can be used to determine this flow rate. One relatively low cost prior art system for determining fluid flow which utilizes such a pressure drop is a so-called pressure rebalance system. In such systems, a port on the high pressure side of the restriction is connected to the input of a centrifugal pump and the pump output is connected to a port on the low pressure side.
A centrifugal pump operating at zero flow produces a head (pressure) which is proportional to the square of the rotational speed of its impeller. Therefore, in a pressure rebalance fluid flow measuring system, the speed of the pump is regulated by a suitable flow rate detector to keep the flow through the pump equal to zero. In this situation the pressure drop through the orifice or venturi is then exactly balanced by and equal to the head produced by the pump and the impeller speed is directly proportional to the volume rate of flow.
Pressure rebalance fluid flow measuring systems of the type broadly described above have proved generally satisfactory for certain applications. A particularly advantageous feature of such pressure rebalance system is their relatively low cost. However, in certain applications their use has been rather severely limited due to various factors including the tendency of the ports to become clogged with particulate matter, and an inability to measure accurately very low fluid flow rates.